1. Field of the Invention
The present invention relates to a thin film magnetic head, and more particularly to a thin film magnetic head having a multilayer structure.
2. Prior Art
Conventionally, a coil conductive layer of the thin film magnetic head makes use of a coil which is wound by the bifilar winding or balance winding.
FIG. 1 is a sectional view showing the thin film magnetic head of the balance winding. In FIG. 1, 1 designates a slider base on which a lower magnetic layer 3 is formed via a lower protective layer 2. On this lower magnetic layer 3, a non-magnetic layer 4 is formed. On this layer 4, a coil conductive layer 6 is formed via an insulating layer 5, where it is sandwiched and surrounded by this insulating layer 5. On the uppermost part of the thin film magnetic head, an upper magnetic layer 7 is formed. The above-mentioned coil conductive layer 6 is formed by a coil 15 which is spiral-wound. In this coil 15 as shown in FIG. 2, a center terminal 8 is provided between a start terminal 10 and an end terminal 9. Further, a first coil 6a is formed between the terminals 8, 9, while a second coil 6b is formed between the terminals 8, 10. The number of turns and winding pitch of the coil 6a are set identical to those of another coil 6b, by which the balanced winding construction is made.
FIG. 3 is a sectional view showing another thin film magnetic head of the bifilar winding. In FIG. 3, as similar to FIG. 1, the lower protective layer 2, lower magnetic layer 3 and non-magnetic layer 4 are formed on the slider base 1 in the upward direction. On the layer 4, three coil conductive layers 11a, 11b, 11c, four insulating layers 12a, 12b, 12c, 12d are formed, on which the upper magnetic layer 7 is further formed. Each of the coil conductive layers 11a, 11b, 11c is configured by each of bifilar-wound coils 17a, 17b, 17c which is made by two conductive coils each having the same number of turns and same winding pitch in parallel. These coils 17a, 17b, 17c are connected together as shown by the dotted lines of FIG. 4 such that the two coils are provided respectively between a center terminal 12 and a start terminal 13 and between a center terminal 12 and an end terminal 14.
In the thin film magnetic head of the balance winding described before, if the coil conductive layer is made as the single layer, two coils should be formed in such single layer, so that the number of turns must be limited. This makes the reproduction output of the thin film magnetic head small. In order to increase the reproduction output, the coil conductive layer can be made as the multi-layer construction by which the number of turns can be increased. However, since the number of turns and winding pitch in the balance winding are set identical in each layer, a step difference like a step of the stairs is formed between the coil conductive layers. This affects the upper magnetic layer so that a discontinuous point is formed in the magnetic circuit. This will reduce the reproduction efficiency. In addition, when the coil conductive layer is made a the multi-layer construction as described above, the diameter of the coil in the lower layer is set identical to that of the coil in the upper layer. Thus, in order to obtain the predetermined inclination at the upper magnetic layer, the length of the lower magnetic layer should be longer, which affects the design of the thin film magnetic head.
Next, in the thin film magnetic head of the bifilar winding, two coils are wound in parallel. Therefore, it is not required that the two coils in each coil conductive layer have the same number of turns. On the other hand, it is required that the terminals ar provided in the two coils in each layer. Therefore, it becomes difficult to store and bury such coil conductive layer within the insulating layer due to the terminals.